The present invention relates to the field of electrical switches, particularly panel switches especially useful for control applications, including on-highway heavy duty trucks and other heavy duty vehicles, off-highway equipment (such as construction equipment and agricultural equipment), marine and automotive applications, for example.
Conventional rocker switches are often used in automotive applications, where it is desirable to provide the vehicle operator with discernible feedback on the position of the switch without distracting the operator from his or her primary function of driving. Such rocker switches have traditionally been designed to switch and carry relatively high amps, typically from about 10 amps to as high as 25 amps. As a result, conventional rocker switches have found wide acceptance in switching virtually every circuit commonly found in the particular application. This proliferation of rocker switches on instrument panels has given rise to a complex and expensive xe2x80x9crats nestxe2x80x9d of large gauge wires behind the panel, which contributes to a similarly complex and expensive wiring harness leading from the panel to the devices being controlled.
One alternative to the foregoing is to xe2x80x9cmultiplexxe2x80x9d the system using a suitable digital data bus. The switches on the panel would be connected to a locally mounted electronics module with short, direct leads or cable assemblies. The local module would then be connected to a remotely mounted control module or power distribution module. The interconnection between the local and remote modules would typically consist of a simple twisted pair of wires instead of the very complex and expensive heavy gauge wiring harness.
However, it has proven difficult to make use of conventional xe2x80x9chigh currentxe2x80x9d rocker switches in the above application. In a very low current application, intermittent operation often occurs, primarily due to the buildup of corrosion and/or oxidation on the contacts of the switch. This corrosion/oxidation layer, while microscopically thin, is sufficient to cause a high contact resistance and inadequate circuit operation in very low current switching applications. The corrosion/oxidation also can yield a leakage current path that can deleteriously impact the performance of digital electronics circuitry. This leakage current is insignificant compared to the many amperes typically carried with a conventional rocker switch, but it is a significant factor compared to the microamps in the digital electronics circuit.
It would therefore be desirable to provide a panel switch having the appearance and ergonomics of a conventional rocker switch that is designed for applications where the current being switched is in the microamp to low milliamp range.
The problems of the prior art have been overcome by the present invention, which provides a switch, especially for heavy duty vehicles, construction and agricultural equipment and automotive applications, configured to meet all types of operator input, including momentary positions, fixed positions, increased intensity back lighting, fixed position illumination, panel markings, push on/push off and audible support. The design utilizes solid state circuitry which minimizes design variations, results in flexible connector choices, requires minimal wiring, and eliminates the failure potential existing in conventional contact dependent switches. In addition, problems associated with high current switching contacts is eliminated by using a low voltage, low current touch pad switch, where the switching occurs directly on a printed circuit board and bulky wire terminations are eliminated. Since contacts only switch very low voltage and very low current, contact wear is virtually non-existent, and the switch can be directly coupled to one or more microprocessors without the need to step down the voltage or current.
The switch of the present invention is typically used in automotive and other control applications, placed in the dash panel an operated by a user by actuating the rocker. When one end of the rocker is pressed, the rocker pivots at its center point fulcrum causing the switch lever, which is housed inside the switch and attached to the rocker, to move in a particular direction. The configuration of the lever is such that the extending ears on opposite sides press against the elastomer seal and move a carbon contact against the integrated circuit traces on a printed circuit board, completing an electrical circuit. This condition occurs for either directional movement of the rocker. Housed within the lever is a spring-loaded plunger fitted with a roller (wheel) at its end. The roller rests on a predesigned detented ramp located as an integral part of the switch insulator.
A sealed elastomer keypad is used to meet the reliability requirements in microamp and low milliamp applications. Actual circuit connectivity is achieved by pressing a carbon-based contact against a set of selectively metal plated interdigitated contact fingers such that the carbon contact causes a xe2x80x9cshortxe2x80x9d across the fingers. The resultant contact resistance is less than 200 Ohms, and is typically in the 10-20 Ohm range.